The invention relates to internal combustion engine valve seals and more specifically to a unitary, i.e., one piece, molded plastic valve stem seal having an elastomeric seal integrally molded thereinto.
In conventional overhead valve internal combustion engines, a pair of valves reciprocate in timed alternation to provide intermittent communication between the intake and exhaust manifolds and a combustion chamber. Lubrication is provided to the upper portions of the valves by a spray of lubricating oil within the valve cover or gravity flow from the associated rocker arm. Oil then flows downwardly along the upper free end of the valve stem toward the valve head. Since temperatures in the combustion chamber may approach or exceed 1000 degrees Centigrade, any lubricating oil exposed to these temperatures will vaporize or burn leaving behind deposits which may interfere with the proper sealing of the valves and cause rapid deterioration thereof.
It is therefore necessary to provide seals generally between the upper region of the valve stems within the valve cover and the valve guide which extends toward the manifolds and combustion chamber. Such a typical valve stem seal takes the form of a cylinder partially closed at one end. The cylindrical region seats about the valve guide to maintain the valve seal stationary and the reduced diameter region slidingly seals against the valve stem.
Extensive effort has been directed to this internal combustion engine component and numerous designs, many of which are patented, are the result of such effort.
For example, many valve stem seals having generally cylindrical bodies of synthetic rubber, for example, Buna N and an annular seal of a distinct material which slidably engages the valve stem have been developed. The annular seal may be fabricated of diverse materials such as cast iron, a synthetic resin or a self-lubricating material such as a tetrafluoroethylene polymer (commercially sold under the trade name Teflon).
Another approach to a valve seal construction utilizes a nylon body with a silicone rubber valve stem engaging grommet which is retained in the seal body by a cooperating T-shaped flange and groove arrangement. Valve seals which comprehend the placement of annular ribs or grooves on the inside of the seal body which improve both the seal against the valve guide and the retention of the valve seal thereon are also known in the art.
The seal itself has also been the subject of design effort and various shapes have been developed for diverse, i.e. non-engine applications. One such design has an X cross section which is fabricated of a natural or synthetic rubber.
From the foregoing review of prior art patents, it is apparent that valve seals conventionally comprise individual body and seal components which typically must be assembled into a valve seal assembly. Such multiple components and associated assembly increases the cost of the units which are utilized in large numbers by internal combustion engine manufacturers. It is therefore apparent that improvements in the art of internal combustion engine valve stem seals are both possible and desireable.